There is currently a strong interest in alternative fuels. These fuels predominantly come from two feedstocks, vegetable oils and sugars. Biodiesel is formed from vegetable oil, and ethanol comes from sugar.
Vegetable oils are mostly comprised of triglycerides, esters of glycerol, CH2 (OH)CH(OH)CH2(OH), and three fatty acids. Fatty acids are, in turn, aliphatic compounds containing 4 to 24 carbon atoms, ideally between 10 and 18 carbon atoms, and having a terminal carboxyl group. Diglycerides are esters of glycerol and two fatty acids, and monoglycerides are esters of glycerol and one fatty acid. Naturally occurring fatty acids, with only minor exceptions, have an even number of carbon atoms and, if any unsaturation is present, the first double bond is generally located between the ninth and tenth carbon atoms. The characteristics of the triglyceride are influenced by the nature of their fatty acid residues.
Biodiesel fuels are fatty acid ethyl and/or methyl esters. These esters are typically prepared by transesterifying triglycerides, the major component in fats and oils, with ethanol and/or methanol, in the presence of an acid or base catalyst. Biodiesel fuels are associated with some limitations. For example, some research indicates that they cause higher emissions of nitrogen oxides (NOx), increased wear on engine components, and fuel injector coking (“Progress in Diesel Fuel from Crop Oils,” AgBiotechnology, (1988)). Also, biodiesel fuel does not provide as much power as petroleum-based diesel is burned (See, for example, Joni, et al., Hungarian Agricultural Engineering, 6:7, 27-28 (1993)), and the diesel engines may need to be retuned in order to run efficiently on biodiesel.
Another effort at producing a renewable fuel has involved the thermal conversion of animal carcasses to a liquid oil product and a water-soluble inorganic product. When animal carcasses are heated, at around 250° C., the triglycerides hydrolyze into glycerol and free fatty acids, and at around 500° C., the free fatty acids decarboxylate to form a mixture of products that relate to the hydrocarbon chains in the original fatty acids. This process is known as thermal decarboxylation.
Most automobiles run on gasoline, and airplanes run on jet fuel, not diesel. It would be advantageous to provide a method for forming alternative fuel sources from vegetable oil feedstocks that have tunable molecular weights and octane or cetane ratings, so that a variety of gasoline, jet fuel, or diesel fuel compositions can be prepared as desired. The present invention provides such methods, as well as renewable gasoline, jet fuel, and diesel fuel compositions.